Could be piston slap, valves, or injectors. I think most common is injectors. I'm convinced I quieted my injectors down when I cleaned them, as they don't make any noise at all now.
I'm working with a friend who has determined that his truck's ticking noise is from noisey injectors. He is goint to clean his injectors as I did and see if it quiets down the same way.
I used two highly recommended products for cleaning varnish out of a fuel system, Schaeffer's Neutra 131 and Lube Control's Fuel Power. I ran the neutra by itself for a few months, then started mixing it with Fuel Power. I now add 2 oz of this brew every time I fill up.
I'll give the injectors a dose of cleaner this weekend. Several posts I just searched have indicated to check the spark plugs. Evidently over time the plugs become loose and need to be retighted. Some have even had problems with blow out plugs if not caught soon enough. I'll check the plugs as well.
I have a ticking too. I really noticed right after installing the Magnacharger. I assumed the worst. Using an auto stethoscope allowed me to determine it was two injectors making the noise. Everything sounded ok. The stethoscope is a handy tool.